Blade for windmill impellers



July25, 1933. E 1,919,588

BLADE FOR WINDMILL IMPELLERS Filed Aug. 30, 1928 will INVEN TOR.

BY WM m azmwwd A TTORNEYS.

Patented July 25, 1933 UNITED STATES PATE NT? OFFICE SPENCER HEATH, or BALTIMORE, MA LAND; ASSIGNOR m, m n AMERICAN PRO- U PELLER COMPANY, OF BALTIMORE, MARYLAND, A CORPORATION or MARYLAND BLADE FOR WINDMILL IMPELLERS of which is set forth upon the accompanying drawing, in which:-

igure 1 is a plan view of an impeller with two blades 1 and 2;

Figures 2 and 3 are elevations of blades 15 1 and 2 of Figure 1; and

Figures 4 and 5 are cross sections on the lines 44 and 5-5 of Figure l-respectively enlarged. V

In the form here illustrated two blades are employed but anynumber or a single blade may be used; in the latter case some firm of counterbalance should be used with:

the single blade.

For the purposes of this invention the blades may be of wood, metal, paper or other composition, solid or hollow-preferably protected by metal sheathing on those ortions most exposed to wear and covered w1th protective coating to resist moistureand corrosion or other weathering effects of exposure.

In the drawing the blades are given the numerals l and 2 and the hub upon which they center and are carried is given the numeral 3. Metal sheathing 4 covers the extreme tip of each blade and extends along the leading edge' nearly to the hub; The direction of the wind is downward against the upward shown flat faces of the blades in Figure l and in the direction of the vertical arrows of Figure 2, 3, 4 and 5. The direction of rotation is indicated by the curved arrow of Figure 1 and by the horizontal arrows of Figures 4 and 5.

In plan form (Fig. 1) the blades are decidedly curved from the hub outwardly, the curvature being opposite in direction from the direction of rotation so that each successive blade cross-section is somewhat rearwardly positioned with respect to the preceding cross-section,. thetip of the blade being narrowest and most rearward. ofall. The leading. edges and portions nearer them are decidedly thicker than the trailing edges and their corresponding portions as shown in Figures 4 and 5 which are typical of sections throughout the blades; 1 Thisgives the blades rigidity along their leading edges and relative flexibility along their trailing edges. An I equal distribution of wind pressure across the blade would therefore cause greater deflection of the trai-lingthan of the leading edgewith increaseof blade angle with-respect to the plane ofgotation but it happens that the greater part of the wind pressure is nearly always nearer to the leading edge, thus tending to increase the deflection of the more rigid. part of the blade perhaps as much or more than thatof the thin trailing edge. I-Iowever, this tendency is much more than'ofi'set by the rearward curvature of blades above described. This curvature places the entire wind pressure ateachcross-section at a more rearward position than atits preceding cross-section.

(considered from the, hub outwards); So great is the combined effect of curvature and relative flexibility at theutrailing edge it is possible to so design and proportion the blade that pressure at any point in the region of the outer half of the blade will cause an increase of all its angles with respect to the planeof rotation. The advantages of a windmill blade so designed are very great in that the blade normally carries arelatively fiat angle to facilitate easy starting and effective operation in winds of low velocity while with: every increase of wind velocity the added pressure on the blade causes it to take aposition of greater angle to its plane of rotation with consequent greater torque or turning effect. The increased angularity of blade position under pressure of the wind is clearly shown by dotted lines in Figures 2, 3, 4 and 5. The reverse changes of blade angle, of course, occur with decreasing wind. The ability to increase blade angles with increasing wind and the reverse with decrease of wind ion erate with less fluctuation of rotational speed under varying winds and to deliver great increase of power from the higher winds without corresponding increase of rotational speed.

In order to obtain still greater change in the angles of the blades in response to chan es in velocity of the wind I employ the Further feature particularly illustrated in Figure 2. Here it will be seen that the blades instead of lying radial] in a flat plane of rotation are given an o lique position, the blades bein set or bent in an axial direction and towar s that side of the lane of rotation on which lies the side 0 the blade receiving impact of the wind. As

shown in the figures this places the fiat sides of the blades at their extremities and outer portions in such positionthat a line connecting them passes clear of the hub on its windward side. In consequence of this oblique positioning of the blades centrifugal force acts upon them with a component in the same direction as the pressure of the wind, thus virtually adding to the pressure of the wind on the flat sides 'of'the blade. This causes still ater deflection of the trailing edges of t e blades than the deflec tion caused by wind pressure alone with consequent further increase in blade angles, the amount of this further increase depending upon the rotational speed, Thus it is seen that the curved plan form combined with the obliqueness of blade position results in a combined action of wind pressure and centrifugal force both for increase of blade angles and consequent greater increase of torque with increasing)wind. This adaptability of the windmill lades to overcome 1ncreasing torque resistances with increases of speed is found of great'service for driving apparatus in which the torque resistance increases rapidly with its rotational speed. This windmill blade is therefore peculiarly adapted for drivin both because of its' acility for starting in low winds and for its ability to more rapidly increase its torque effect with increase of wind and rotational velocity; r

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A windmill impeller having blades, each of said blades being flat on one side and convex on the other side, said blades having electric generators,

an axial inclination towards that side of the plane of rotation on which lies the flat side of the blade.

V 2. A windmill impeller having blades, each of said blades being curved in a direction opposite from its direction of rotation and having an axial inclination towards that side of the plane of rotation on which lies the side of t e blade receiving impact of the wind. 4

3. A- windmill impeller having blades, said blades being curved in a direction opposite from their direction of rotation and havin their leading edges relatively ri id and t eir trailing edges relatively flexihle and said blades having an axial inclination towards that side of the plane of rotation on which lies the side of the blade receiving impact of the wind.

4. A windmill impeller having blades, said blades having leading edges and trailing edges, said edges being curved in a direction opposite from their direction of rotation and said leading edges being of greater curvature than said trailing edges and said blades having an axial inclination towards that side of the plane of rotation on which lies the side of the blade receiving impact of the wind.

5. A windmill impeller having blades, said blades having leading edges and trailing edges, said edges being curved in a direction opposite from their direction of rotation and said leading edges being of greater curvature and less flexibility thansaid trailing edges and said blades havin an axial inclination towards that side of the plane of rotation on which lies the side of the blade receiving impact of the wind.

6. A windmill impeller having blades, said blades being formed of portions varying in flexibility, the said blades being axially inclined forwardly so that'they will increase their face angularity in direct response to centrifugal force.

7 An impeller blade for windmills hav-, ing its leading edge relatively rigid and its trailing edge relative flexible, so that pressure of the wind causes greater deflection of the trailing edge of the blade, the lonitudinal axis of said blade being inclined iorwardly with respect to its plane of rotation, so that said blade will increase its face angularity in response to centrifugal fonce.

SPENCER -HEATH. 

